For both my pregnancies, my milk came in 3 days after delivery. TRUST me you will know! They get HUGE, FULL, and HARD! LOL! At this point you will also probably need to (depending on your supply), be careful of letdown. I had to literally walk around with cups if I was braless, or stood up braless! LOL! It would just pour out of me. Although, this last time (with my son) I had a huge supply...8-13oz per pumping. I couldn't breastfeed directly due to him being a preemie. Anyway...you will see possibly just colostrom (like said above) coming out until and for the first day or so after delivery. You may be having it and not knowing....you can try to express some just by squeezing your nipple. It will be clear/yellowish. Good luck and happy nursing!